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In this paper we compare numerical results for the ground state of theHubbard model obtained by Quantum-Monte-Carlo simulations with results fromexact and stochastic diagonalizations. We find good agreement for the groundstate energy and superconducting correlations for both, the repulsive andattractive Hubbard model. Special emphasis lies on the superconductingcorrelations in the repulsive Hubbard model, where the small magnitude of thevalues obtained by Monte-Carlo simulations gives rise to the question, whetherthese results might be caused by fluctuations or systematic errors of themethod. Although we notice that the Quantum-Monte-Carlo method has convergenceproblems for large interactions, coinciding with a minus sign problem, weconfirm the results of the diagonalization techniques for small and moderateinteraction strengths. Additionally we investigate the numerical stability andthe convergence of the Quantum-Monte-Carlo method in the attractive case, tostudy the influence of the minus sign problem on convergence. Also here in theabsence of a minus sign problem we encounter convergence problems for stronginteractions.Comment: 24 pages, 9 figure

Comparison of Calculations for the Hubbard Model Obtained with Quantum-Monte-Carlo, Exact, and Stochastic Diagonalization